1. Field of the Invention
The invention relates to a holder for connecting a blade to the lower edge of a snow-clearing device, such that the blade is given a cutting (acute) angle to the base and can be folded backwards, thereby avoiding damage when running into an obstacle, and automatically resume its cutting angle after passing the obstacle.
2. Description of the Related Art
In the first place, the invention is intended for use on a snow-clearing device comprising a plough wing, snow scraper or snow blade which is supported by a vehicle or device carrier of some type and which in its lower part has at least one blade serving to engage the ground with its cutting edge and ensure a snow-cutting and snow-raising action. Use is normally made of a plurality of relatively short blades which are mounted side by side along the lower edge of the snow-clearing device.
It is desirable that the device can remove substantially all loose snow lying on a roadway, i.e. as far as possible also snow lying in cavities in the form of e.g. ruts in the roadway, to provide a safe base. This means that the blades of the snow-clearing device must be able to operate in close engagement with the roadway, which can be achieved if they are flexibly fixed to the lower part of the plough and thus can be individually inclined in the lateral direction relative to the lower part of the plough. It is also desirable that the device can cut or scrape away snow or ice adhering to the roadway. Moreover, it should be possible to carry out the above-mentioned snow-clearing work at high speed. It goes without saying that snow-clearing under these conditions subjects both the snow-clearing device and the device carrier to heavy stress, and they can be damaged if the blade strikes against a stationary obstacle, for instance, protruding gutters, kerbs, and railway tracks.
To protect the device and the device carrier against damage arising in case of running into an obstacle, it is previously known to mount the blade to be pivotable backwards, against the action of a spring, about a hinge located above the blade. In this case, the blade must be essentially vertically oriented to the roadway, thereby making it possible for the lower edge of the blade to move backwards/upwards without causing a lifting motion of the device. It is not possible to position the blade at an evidently positive angle relative to the vertical plane, i.e. with the lower edge of the blade extended forwards in the travelling direction. With this design, the blade therefore operates with a scraping effect against the roadway, thereby making it necessary to press the blade against the roadway relatively firmly to ensure good snow-clearing results. The construction also results in the snow-throwing ability being limited.
A prior-art arrangement for protecting devices and device carriers when the blade is oriented at an acute, cutting angle to the roadway is disclosed in International Patent Application WO 95/23894. The blade is hingedly attached to the front end of a forwardly extended pivot arm. When running into an obstacle, the blade can, against the action of a spring, be folded backwards while at the same time the pivot arm is raised against the action of another spring. In this construction, the blade has a positive angle relative to the vertical plane and also vertical flexibility relative to the roadway. However, a drawback is the fact that the blades cannot be inclined in the lateral direction and, thus, do not achieve the flexibility that is required to obtain a good snow-clearing effect on a rutted roadway. Besides, the mechanical construction requires much repair and maintenance since it is subjected to heavy wear and is easily damaged in this environment.